1. Field of the Invention
This invention relates broadly to apparatus and methods for submarine photography. More particularly, it concerns improvements in such apparatus and methods that inform the system when a photographic subject is in the camera's field of view and that the distance to the subject is suitable for in-focus photography.
2. Description of the Prior Art
A great number of underwater photographs are taken with cameras which have limited remote controls. This is particularly true of deep-sea 35 mm. camera systems where camera lens opening and focus are preset and the photographer must somehow arrange for the subject to be at the correct distance and within the field of view at the time of exposure.
One approach to providing better control in submarine photography would be to incorporate the ranging features of advanced, above the surface (surface) cameras. Such cameras use a variety of techniques to obtain proper exposure conditions for control. The most common is a triangulation arrangement which superimposes the images received by a pair of space optical receivers and provides automatic, mechanical adjustment of the lens until the received images are coincident. Microelectronics are used to perform the image comparison and thereby provide automatic focusing (see U.S. Pat. Nos. 3,435,744 and 4,313,654).
Other advanced surface cameras use microprocessor based optical-image analyzers to determine correct focus. Also, sonar systems are used in some cameras.
The optical systems of the surface cameras generally use infrared light beams with reflected light intensity, image analysis and triangulation. Unfortunately, the devices and techniques developed for surface cameras are not directly transferable to submarine camera systems. Differences between the physical properties of air and water result in major differences in the propagation of light and sound in the two media. Additionally, spurious material and signals can cause many "false" exposures to occur with submarine photography while this is not a serious consideration in use of surface cameras. Therefore, a camera system which depends on the propagation of energy waves for operation must be designed for the medium in which it is to be used.
Extensive development work has occurred relative to submarine photography, e.g., see "Underwater Photography--Scientific and Engineering Applications", compiled by Paul Ferris Smith, Van Nostrand Reinhold Company, 422 p., 1984. Such work has included use of (a) optical triggering of underwater cameras, e.g., see U.S. Pat. No. 3,446,555 and pp. 223-228, "Deep Sea Photography", J. B. Hersey, Editor, The Johns Hopkins Press, 1967, and (b) sonar techniques, e.g., see U.S. Pat. Nos. 4,105,990; 4,335,944; 4,381,144 and 4,447,896.
Notwithstanding the extensive prior work and developments with surface and submarine camera systems, substantial improvements are needed for the submarine systems, e.g., to provide for (1) more efficient use of battery or other power, (2) saving of film and (3) mitigation of triggering of exposure by spurious materials or events.